Attribute “xmlns:svg” not allowed here.

In HTML5, SVG elements are natively supported and don’t require explicit namespace declarations at all. When you write an <svg> tag inside an HTML document, the browser automatically associates it with the correct SVG namespace (http://www.w3.org/2000/svg). The xmlns:svg="http://www.w3.org/2000/svg" attribute is a prefixed namespace binding — it declares svg as a namespace prefix — which is a concept from XML/XHTML workflows that HTML5’s parser does not support or recognize.

The HTML specification defines a limited set of allowed attributes on each element. Since xmlns:svg is not among them for the <svg> element (or any HTML5 element), the W3C validator flags it as invalid. The only namespace-related attribute the HTML parser tolerates on <svg> is xmlns="http://www.w3.org/2000/svg", and even that is optional — it’s accepted purely for compatibility with XHTML but has no functional effect in HTML5.

This issue commonly appears when SVG code is exported from graphic editors like Inkscape or Adobe Illustrator, or when SVG files originally written as standalone XML documents are pasted directly into HTML. These tools sometimes include verbose namespace declarations that are necessary in XML contexts but invalid in HTML.

Why it matters

• Standards compliance: The HTML5 specification explicitly does not allow prefixed namespace attributes. Using them results in validation errors.
• Code cleanliness: Unnecessary attributes add clutter without any benefit, making your markup harder to read and maintain.
• Potential parsing issues: While most browsers silently ignore unrecognized attributes, relying on lenient browser behavior rather than valid markup can lead to unexpected results in edge cases or non-browser HTML consumers (e.g., email clients, content scrapers, or accessibility tools).

How to fix it

1. Locate all <svg> elements in your HTML that contain the xmlns:svg attribute.
2. Remove the xmlns:svg="http://www.w3.org/2000/svg" attribute entirely.
3. If you’re working in an HTML5 document (not XHTML), the xmlns="http://www.w3.org/2000/svg" attribute is also optional — you can keep or remove it.
4. If your SVG uses other prefixed namespace declarations like xmlns:xlink, consider replacing them with their HTML5 equivalents (e.g., use href instead of xlink:href).

Examples

Incorrect: using xmlns:svg on an SVG element

The xmlns:svg attribute triggers the validation error:

<svg xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

Correct: removing the prefixed namespace

Remove xmlns:svg and keep only the standard attributes:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

Also correct: minimal inline SVG in HTML5

In HTML5, the xmlns attribute itself is optional for inline SVG, so this is the cleanest approach:

<svg viewBox="0 0 100 100">
  <circle cx="50" cy="50" r="40" fill="blue" />
</svg>

Cleaning up multiple unnecessary namespaces

SVG exported from editors often includes several unnecessary namespace declarations. Here’s a before-and-after of a typical cleanup:

Before (multiple invalid namespace attributes):

<svg xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 200 200">
  <image xlink:href="photo.jpg" width="200" height="200" />
</svg>

After (cleaned up for HTML5):

<svg viewBox="0 0 200 200">
  <image href="photo.jpg" width="200" height="200" />
</svg>

Note that xlink:href has been replaced with href, which is the modern standard supported by all current browsers. The xmlns:xlink declaration is no longer needed either.

Learn more:

MDN Reference

MDN: Namespaces crash course

→

MDN Reference

MDN: Introduction to SVG

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